He told MEPs in Strasbourg: "If the UK Government sticks to its decision to leave, Brexit will become a reality - with all its negative consequences - in March next year unless there is a change of heart among our British friends.

"Wasn't it David Davis himself who said 'if a democracy cannot change its mind, it ceases to be a democracy’?"

He added the EU had not had a "change of heart" over Brexit, telling the British: "Our hearts are still open to you."

European Commission president Jean-Claude Juncker backed Mr Tusk's message, saying he hoped it "will be heard clearly in London".

Boris Johnson finally admits there was an error on the Vote Leave bus - that the £350m a week claim was too LOW

The Tory government, whose Brexit Secretary is Mr Davis, has said bluntly that there will not be a second EU referendum.

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Donald Tusk (right) declared: "Our hearts are still open to you" (Image: AFP)

David Davis's government says bluntly that there will not be a second EU referendum (Image: AFP)

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Labour MP Ian Murray, a backer of the anti-Brexit Open Britain group, said: "Until we've actually left, Brexit is a reversible process, that much is clear. If people decide that Brexit isn't the right path for the country, they have the right to change their minds.

“The point has been made by legal experts, EU leaders and even the architect of Article 50, Lord Kerr. The Government should now be upfront with the public and publish its own legal advice on the matter."

But Tory Brexiteer MP Bernard Jenkin fumed: "Nobody serious wants another referendum in this country on this question.

"It’s absurd. The referendum was won by the Leave campaign against the odds and against the expectation because nobody could find anything good to say about the EU."

Jeremy Corbyn and Labour figures have failed to rule one out in future (Image: PA)

Mr Tusk and Mr Verhofstadt both demanded more clarity from Theresa May over her Brexit plans after she reached a first-round deal over citizens' events, Northern Ireland and the £39billion 'divorce bill' in December.

Mr Tusk said: "As regards our future relations, what we need today is more clarity on the UK's vision.

"Once we have that, the leaders will meet and decide on the way the EU sees its future relationship with the UK as a third country.”

Calling for continued unity among the remaining 27 members of the EU, he said: "The hardest work is still ahead of us and time is limited.

"We must maintain the unity of the EU27 in every scenario, and personally I have no doubt that we will.”

Mr Verhofstadt said the rights of citizens - including on free movement - should continue to apply until the transition period ends.

Draft negotiation guidelines, leaked last night, showed EU leaders were set to demand migrants who arrive in Britain right up to the end of the decade be allowed permanent residency.

MEPs ridiculed the promise to bring back blue passports as a 'scam' (Image: PA)

Conservative MEP Syed Kamall admitted the second phase of negotiations would be no easier than the first.

"There will probably be moments when it seems like the two sides are far apart, incapable of understanding each other," he told MEPs.

But for all the spirit of co-operation MEPs also ridiculed Theresa May's "scam" to bring back blue passports after Brexit.

Mr Verhofstadt said the situation over passports was a "whole hilarious thing".

Senior German MEP Manfred Weber, a key ally of Chancellor Angela Merkel, added: "The whole story is a scam, EU law does not say anything about passport colours."

The comments came as Remain backing MPs were set to make a last-ditch bid to scupper Brexit today as the EU Withdrawal Bill reaches its final stage of the House of Commons.

Pro-EU rebels from both sides of the Commons are expected to lay down amendments which could stall or wreck the Government’s plan for Brexit.

One amendment, laid down by Labour’s Chuka Umunna, would force the government to reveal legal advice given to the government last year, which Remainers believe told them Article 50 was reversible.

The amendment last night had cross-party support from a growing number of MPs.